Worm gear drives are used for transmitting power from an input shaft to an output shaft which are non-intersecting and typically disposed at a right angle to each other. As known in the art, worm gear drives include a toothed gear, which is attached to the output shaft, and a threaded worm mounted onto the input shaft. Correspondingly, the gear teeth mesh with the worm threads in predominately a sliding manner.
Worm gear drives are advantageous over other drive methods because of their conjugate tooth action, arrangement, compactness, and load capacity. Correspondingly, worm gear drives are used in applications where heavy shock loading can be encountered and a high degree of precision power transfer is desired.
The mesh between the gear teeth and the worm threads must be carefully designed, manufactured, and maintained in order to yield a constant output speed between the input shaft and the output shaft. Backlash, also know as "play," occurs when some or all of the gear teeth do not perfectly mesh with the worm threads. Stated in other terms, backlash is the amount by which the width between the worm threads exceeds the thickness of an engaging gear tooth. Correspondingly, the amount of exhibited backlash may vary substantially as various teeth on the gear are moved into engagement with the threads on the worm.
Backlash can be caused by a poor initial design, inaccurate machining, improper assembly, or normal wear between the worm threads and the gear teeth. However, as indicated previously, backlash must be minimized if a high degree of precision is desired between the output shaft and the input shaft.
Accordingly, many designs have been offered for reducing backlash by making periodic adjustments to diminish the gap between the intermeshing gear teeth and worm threads. However, these periodic adjustments are only made when the amount of backlash exceeds a predetermined tolerance level. Correspondingly, between each adjustment period, backlash below the maximum tolerance level is allowed to persist.
In addition, any adjustments to reduce backlash must be performed manually. The adjustments are made after the worm gear drive has been taken out of service or, during service, but only if the drive is equipped with a specially designed input shaft that allows for axially repositioning while in use.
Furthermore, none of the present worm gear designs can effectively eliminate backlash if the teeth on the gear vary in thickness. Instead, the prior gear designs are only capable of ensuring that no gap exists when the thickest gear tooth is engaged by the threads of the worm. Therefore, backlash still exists as narrower gear teeth are engaged by the worm threads.
Correspondingly, the present invention provides a device which overcomes the above-discussed problems by eliminating or substantially dampening the presence of backlash within a worm gear drive as gear teeth are engaged by the worm threads.